In recent years, driven by the demand of vehicle indoor navigation and personal mobile navigation, an inertial measurement unit (IMU) has gradually become an auxiliary system for navigation apparatuses. For instance, when a vehicle enters a tunnel or an underground parking lot, or when a pedestrian walks into a building, the global positioning system (GPS) in the navigation apparatus may be affected by a shielding effect such that the navigation apparatus may temporarily not be able to receive a position signal from a satellite.
In the above situations, the navigation apparatus cannot obtain sufficient signals from the satellite, and therefore cannot find the accurate position of a user. As a result, accurate navigation information cannot be provided. On the other hand, if the measurement data of the IMU is provided, the navigation apparatus can continue to provide position information and navigation information in places where a GPS signal cannot be received. Therefore, a navigation apparatus integrating the IMU and the GPS has become the next major competitive product in the market.
Regarding current techniques, the traditional micro-electromechanical IMU mainly contains a three-axis accelerometer and a three-axis gyroscope. The three-axis gyroscope includes an oscillator and three Coriolis accelerometers. The oscillator needs to be able to oscillate in two perpendicular directions on the same plane at the same time. To prevent the sensing signals of the three-axis accelerometer and the three-axis gyroscope from interfering with each other, the IMU adopts a design in which three masses of the accelerometer and three masses of the gyroscope are capable of moving independently. However, the design has the disadvantage of having excessive overall area of the IMU because no common mass is used in the design.
In the known techniques, a hollow disc-like oscillator of the gyroscope can be rotated to generate an oscillation in two perpendicular directions on the same plane at the same time. Since the hollow disc-like oscillator generally rotates by taking an element located on the axis of rotation as a pivot, an additional sensor such as accelerometer cannot be disposed in the central region of the disc-like oscillator.
FIG. 1A is a schematic diagram of a simplified X-axis accelerometer. Referring to FIG. 1A, when an accelerometer 10 senses an acceleration Ax in the direction parallel to the X-axis, the distance between a fixed electrode 14 and a moving electrode 15 is changed, causing a change in capacitance. Therefore, the value of the acceleration Ax can be calculated by sensing the change of capacitance between the fixed electrode 14 and the moving electrode 15.
FIG. 1B is a schematic diagram of a simplified Y-axis accelerometer. Referring to FIG. 1B. When an accelerometer 20 senses an acceleration Ay in the direction parallel to the Y-axis, the capacitance between a fixed electrode 24 and a moving electrode 25 is changed. Therefore, the value of the acceleration Ay can be calculated by sensing the change of capacitance between a fixed electrode 24 and a moving electrode 25.
FIG. 1C is a schematic diagram of a simplified Z-axis accelerometer. Referring to FIG. 1C, when an accelerometer 30 senses an acceleration Az in the direction parallel to the Z-axis, a mass 33 connected to a fixed end 32 via a torsion beam 31 rotates about the torsion beam 31 (i.e., the axis of rotation is parallel to the Y-axis), similar to the swinging of a seesaw, such that the capacitance between the fixed electrode 34 and the moving electrode 35 is changed. Therefore, the value of the acceleration Az can be calculated by sensing the change of capacitance between the fixed electrode 34 and the moving electrode 35.
In general, the torsion beam 31 is disposed on two opposite sides of the mass 33, and a connecting line 31a between the two torsion beams 31 does not pass through a center of mass 33a of the mass 33. In other words, the torsion beam 31 is, for instance, eccentrically disposed on the mass 33 to improve the sensitivity of the accelerometer 30. Moreover, in a related art (not shown), the torsion beam can also be connected to the mass and the fixed end along the direction parallel to the X-axis. When the accelerometer occurs in the direction parallel to the Z-axis, the mass rotates about the torsion beams (i.e., the axis of rotation is parallel to the X-axis), similar to the swinging of a seesaw. Under such configuration, the accelerometer can also calculate the value of acceleration in the direction parallel to the Z-axis.
The accelerometers 10, 20, and 30 can respectively be used for measuring acceleration in the directions parallel to the X-axis, the Y-axis, and the Z-axis. Therefore, a three-axis accelerometer can be formed by integrating the accelerometers 10, 20, and 30 into a single apparatus.
FIG. 2A is a schematic diagram of a simplified X-axis gyroscope. Referring to FIG. 2A, a spring 41 is connected to an anchor 42 and a frame 43, and a torsion beam 44 is connected to the frame 43 and a mass 45. The frame 43 oscillates along the direction parallel to the Y-axis so as to drive the mass 45 to oscillate along the direction parallel to the Y-axis. When the gyroscope 40 senses an angular velocity Rx in the direction parallel to the X-axis, the mass 45 rotates about the torsion beam 44 (i.e., the axis of rotation is parallel to the X-axis). Therefore, the capacitance between the mass 45 and electrode (not shown) on the substrate (not shown) is changed. The value of the angular velocity Rx can be calculated by sensing the change of capacitance caused by the rotation of the mass 45.
FIG. 2B is a schematic diagram of a simplified Y-axis gyroscope. Referring to FIG. 2B, a spring 51 is connected to an anchor 52 and a frame 53, and a torsion beam 54 is connected to the frame 53 and a mass 55. The frame 53 oscillates along the direction parallel to the X-axis so as to drive the mass 55 to oscillate along the direction parallel to the X-axis. When the gyroscope 50 senses an angular velocity Ry in the direction parallel to the Y-axis, the mass 55 rotates about the torsion beam 54 (i.e., the axis of rotation is parallel to the Y-axis). Therefore, the capacitance between the mass 55 and electrode (not shown) on the substrate (not shown) is changed. The value of the angular velocity Ry can be calculated by sensing the change of capacitance caused by the rotation of the mass 55.
FIG. 2C is a schematic diagram of a simplified Z-axis gyroscope. Referring to FIG. 2C, a spring 61 is connected to an anchor 62 and a frame 63, and a spring 64 is connected to the frame 63 and a mass 65. The frame 63 oscillates along the direction parallel to the Y-axis so as to drive the mass 65 to oscillate in the direction parallel to the Y-axis. When the gyroscope 50 senses an angular velocity Rz in the direction parallel to the Z-axis, the mass 65 translates in the direction parallel to the X-axis. Therefore, the value of the angular velocity Rz can be calculated by sensing the change of capacitance between the fixed electrode (not shown) on the substrate (not shown) and the moving electrode (not shown) on the mass 65.
FIG. 2D is a schematic diagram of another simplified Z-axis gyroscope. Referring to FIG. 2D, a spring 71 is connected to an anchor 72 and a frame 73, and a spring 74 is connected to the frame 73 and a mass 75. The frame 73 oscillates along the direction parallel to the X-axis so as to drive the mass 75 to oscillate along the direction parallel to the X-axis. When the gyroscope 70 senses the angular velocity Rz in the direction parallel to the Z-axis, the mass 75 translates in the direction parallel to the Y-axis. Therefore, the value of the angular velocity Rz can be calculated by sensing the change of capacitance between the fixed electrode (not shown) on the substrate (not shown) and the moving electrode (not shown) on the mass 75.
The gyroscopes 40, 50, and 60 (or 70) can respectively be used for measuring the angular velocity in the directions parallel to the X-axis, Y-axis, and Z-axis. A three-axis gyroscope can be formed by integrating the gyroscopes 40, 50, and 60 (or 70). A six-axis IMU needs to integrate the three-axis accelerometer and the three-axis gyroscope into a single apparatus.
In the current techniques, the IMU can adopt (1) a design of sharing a common mass (i.e., the accelerometer and the gyroscope use the same proof mass) or (2) a design of applying independent masses (i.e., the accelerometer and the gyroscope use different proof masses). FIG. 3 is a schematic diagram of a known IMU, wherein the accelerometer and the gyroscope adopt the design of sharing a common mass. FIG. 4 is a schematic diagram of a known IMU, wherein the accelerometer and the gyroscope adopt the design of applying independent masses.
Referring to FIG. 3, a common mass 81 of an IMU 80 is surrounded by an electrode 82 for radial control, a rotor 83, and an electrode 84 for radial control, wherein a common electrode 85 is between any two adjacent electrodes 84 for radial control. Since the IMU 80 uses the same mass 81 as a common mass for detecting accelerations in three axes and angular velocities in two axes, the IMU 80 has the disadvantages of coupling noise of sensing signal and complexity of readout circuit design.
Referring to FIG. 4, an IMU 90 is formed by a three-axis gyroscope 91 and a three-axis accelerometer 92, wherein the three-axis gyroscope 91 and the three-axis accelerometer 92 are independent sensing structures which apply independent masses. More specifically, the three-axis gyroscope 91 is formed by three independent angular velocity sensing structures 91a, 91b, and 91c which are respectively used for detecting angular velocities in three axes. Moreover, the three-axis accelerometer 92 is formed by three independent acceleration sensing structures 92a, 92b, and 92c which are respectively used to detect accelerations in three axes. Each of the three angular velocity sensing structures 91a, 91b, and 91c uses an independent oscillating frame respectively, and the three acceleration sensing structures 92a, 92b, and 92c also do not use a common mass. As a result, the IMU 90 has the disadvantages of, for instance, large footprint area and high manufacturing costs.
FIG. 5 is a schematic diagram of a known three-axis gyroscope. Referring to FIG. 5, U.S. Pat. No. 7,694,563 discloses a micro-electromechanical three-axis gyroscope 100. The micro-electromechanical three-axis gyroscope 100 uses a hollow disc-like structure 110 as an oscillator. A pivot element 111 of the oscillator is disposed in the center of the hollow disc-like structure 110. Accordingly, the hollow disc-like structure 110 drives masses 120, 130, and 140 to rotate about the Z-axis to sense angular velocities in three axes.
FIG. 6 is a schematic diagram of a known differential gyroscope. Referring to FIG. 6, US Patent US 20100132460 discloses a differential gyroscope 200. When a mass 230 is driven, the mass 230 moves in the opposite direction to sense an angular velocity.